Every so often, without swinging a pick or lifting a shovel, professional diggers discover scientific treasures. Browsing through the modest collections of amateur "rock hounds," they have found many a rare fossil, often misclassified and almost as obscure as if it were still buried in prehistoric shale. Last winter, hoping for just such a find, veteran Paleontologist George Gaylord Simpson took time out from a lecture tour to visit the private museum of Alonzo Wesley Hancock, a retired Oregon postman.
An amateur archaeologist ever since he was a boy in the Ozarks, 69-year-old Digger Hancock showed his visitor an array of...